1. Field of the Invention
This invention relates to fuel injection control apparatus and method for a direct injection internal combustion engine in which fuel is injected from a fuel injection valve directly into an engine combustion chamber.
2. Description of the Related Art
Normally with fuel injection control in a direct injection internal combustion engine, operation of the fuel injection valves is controlled in response to a target injection quantity that is calculated based on the operating state of the engine, such as engine speed and engine load. The fuel injection quantity is then adjusted to an amount that is suitable for the engine operating state at that time.
An apparatus for performing this kind of fuel injection control, which increase-corrects the fuel injection quantity at start-up when the engine is cold is widely known (see JP(A) 2004-225658, for example). This increase correction is performed to both improve the combustion state and facilitate early warming-up of an exhaust gas control catalyst provided in the engine exhaust passage.
Furthermore, a fuel injection control apparatus is also known which switches the fuel injection mode between a batch injection in which the fuel is injected all at once, and a split injection in which the fuel is injected in a plurality of separate injections (see JP(A) 2003-65121, for example). Switching the fuel injection mode in this way enables the fuel injection state to be finely controlled in a manner appropriate for the engine operating state and the engine temperature and the like.
In a fuel injection control apparatus that performs an increase correction, such as that described above, however, the following problems occur when performing fuel injection control while switching between a batch injection and a split injection.
That is, the amount of fuel that actually contributes to combustion may be less than the amount of fuel injected from the fuel injection valve due to some of the injected fuel adhering to the inside wall of the engine combustion chamber when the engine is cold. As a result, the amount of fuel that actually contributes to combustion changes, which affects the combustion state. Also, the amount of fuel that adheres to the inside wall of the engine combustion chamber changes depending on the fuel injection timing. This is because the area of the inside wall that is exposed in the combustion chamber changes as the engine piston (hereinafter simply referred to as “piston”) moves, and the position of the piston changes depending on the fuel injection timing. Moreover, in addition to the fuel injection timing, the period of time between when fuel is injected and when it is ignited, i.e., the time required for the fuel to vaporize, differs which also affects the amount of fuel that adheres.
Also, the direction of movement and the speed of the piston, or the actual volume of the combustion chamber, differs depending on the fuel injection timing, which affects the extent to which injected fuel is vaporized. As the extent to which injected fuel is vaporized changes, the amount of fuel that actually contributes to combustion also changes, which in turn changes the combustion state.
Therefore, even if the amount of fuel is increased in the same way when a batch injection is performed as it is when a split injection is performed, the amount of fuel contributing to combustion is different. Thus there still remains room for improvement in this area.